Handle addresses of more constants in IPA-CP

Handle addresses of more constants in IPA-CP

IPA-CP can handle addresses of scalar constants (CONST_DECL) so this extends
that to addresses of constants in the pool (DECL_IN_CONSTANT_POOL).  Again
this is helpful for so-called fat pointers in Ada, i.e. objects that are
semantically pointers but represented by structures made up of two pointers.

This also moves the unused function print_ipcp_constant_value from ipa-cp.cc
to ipa-prop.cc and renames it.

gcc/
	* ipa-cp.cc (print_ipcp_constant_value): Move to...
	(values_equal_for_ipcp_p): Deal with VAR_DECLs from the
	constant pool.
	* ipa-prop.cc (ipa_print_constant_value): ...here.  Likewise.
	(ipa_print_node_jump_functions_for_edge): Call the function
	ipa_print_constant_value to print IPA_JF_CONST elements.